Production of a network of polyacrylonitrile filaments



United States Patent Oifice 3,433,866 Patented Mar. 18, 1969 7 Claims ABSTRACT OF THE DISCLOSURE A tow of stretched polyacrylonitrile filaments containing 100-300 parts by weight of water and at least 0.5 part by weight of solvent is opened and subjected to a moist atmosphere wherein the wet bulb temperature is 65-120 C. to produce a network useful for the protection of crops.

This invention relates to the production of a filamentary structure which can be laterally extended to form a network.

It is known to secure together adhesively, over their entire length, a set of parallel artificial or synthetic filaments in order to form yarns or ribbons. This is effected by impregnating the filaments, after their formation, with a solvent, a latent solvent, or a swelling agent, or even a dilute solution of a cellulose derivative as an adhesive for filaments of the same material.

It is also known to produce artificial or synthetic yarns whose constituent filaments are lightly adhesively secured together at intervals, by dry spinning, employing spinnerets whose orifices are situated very close to one another, and by slightly modifying the spinning conditions. In this way yarns are obtained whose constituent filaments, being lightly stuck together, are maintained in position when one of them breaks. The subsequent working of the yarns, for example by twisting, weaving or knitting, is therefore not affected by the breakage of a single filament, as frequently occurs under the usual working conditions.

It is-also known to obtain nets of artificial or synthetic material by spinning through two series of orifices moving relatively to each other in a direction transverse to the direction of extrusion, so that the orifices of the two series are periodically in register. In this way there is obtained a network in which the dimensions of the meshes are dependent on the periodicity of the movement of the two series of orifices.

According to the present invention, a filamentary structure capable of being laterally extended to form a tow is made by subjecting a tow of stretched acrylonitrile polymer filaments, in which the acrylonitrile content of the polymer is at least 70%, and which are in the formof an aqueous gel containing, for each 100 parts of polymer (reckoned as dry) 100-300 parts of water and at least 0.5 part of an organic solvent for the polymer, to a temperature of at least 65 C. in a moist atmosphere.

Parts and percentages are by weight throughout.

By acrylonitrile polymers are meant the homopolymers of acrylonitrile, and also copolymers, graft copolymers and mixtures of polymers containing at least 70% of acrylonitrile and up to of one or more ethylenic monomers copoly-merisable therewith, such as vinyl compounds, for example vinyl chloride and acetate, acrylic and methacrylic acids, esters and amides, methacrylonitriles, vinyl sulphonic compounds such as sulphonated aromatic derivatives, for example styrene sulphonic acid or vinyl hydroxyarenesulphonic acids, other vinyl derivatives of basic type such as vinyl pyridine and its alkyl derivatives, and vinyl ethers of dialkylamines.

The filaments in the form of an aqueous gel which are used in carrying out the invention are advantageously obtained by wet spinning into an aqueous coagulating bath. They must have been stretched to give them sutficient strength to make possible their subsequent manipulation in the course of the process of the invention, advantageously 1.5-1.8 or more times their initial length. This stretch may be imparted to them in the spinning zone, namely the coagulating bath or the dry spinning cell, in accordance with the process by which they are obtained. The filaments may undergo a further stretch, which may be of greater extent than the first after they have been washed and before they are treated in accordance with the invention.

The filaments in the form of the aqueous gel must contain at least 0.5%, and preferably contain 15%, calculated on the weight of the dry polymer, of an organic solvent, usually that which has been used for shaping them; contents up to 20% and 30% may also be suitable, and even be exceeded.

The organic solvent employed may be chosen from the usual organic solvents used in the manufacture of acrylic fibres. There may be mentioned by way of example the N-formylated amines such as dimethylformamide, and among the many other known solvents dimethylsulphoxide, -butyrolactone, and dimethylacetamide, etc. Of course, mixtures of these various substances with one another or with other products may be employed.

In carrying out the process of the invention, it is necessary for the filaments to be treated at a temperature of at least 65 C. Since the filaments are in the form of an aqueous gel which it is desirable to dry, it is advantageous to carry out the treatment during the drying. In order that the temperature of the wet filaments may be at least equal to 65 C. in an industrial drying chamber, which is necessarily ventilated, the wet bulb temperature of the dryer should also be at least equal to 65 C. On the other hand, the dry bulb temperature of the treatment chamber may vary within wide limits without modifying to any considerable extent the result obtained. It is generally advantageous, for reasons of economy and ease of application, that this temperature should not be maintained too high; it may be, for example, C.- 0., although C. may be reached and even exceeded.

The duration of the treatment may vary within wide limits, and may be readily adjusted by the operator in accordance with the dry and wet bulb temperatures employed, the size of the tow treated and the result aimed at.

The treatment may be carried out on a tow for-med of a large number of filaments, for example at least 5000, and it is generally preferred to apply it to tows of from 30,000 to 150,000 filaments; however these figures have no limiting character, and the size of the tow must be chosen in accordance with the use to which the network is to be applied. It is generally advantageous to open the tows of parallel filaments before they are treated, for example by means of an air jet.

The process of the invention makes it possible to obtain tows whose constituent filaments are adhesively secured together in an irregular manner and from place to place, giving a product that can be opened out into a very wid continuous network, often several metres wide, for example for the protection of crops from insects or other pests.

The tow obtained in accordance with the invention may be given any desired further treatment, such as stretching, setting, crimping, finishing, dyeing or dressing, provided that care is taken to avoid impairing th structure or appearance of the product. Some of these treatments may be applied in order further to enhance the effect of the process of the invention; for example crimping, by taugling the filaments, further increases the effectiveness of the network obtained when the tow is opened out laterally.

The following examples illustrate the invention.

Example 1 A tow of 15,000 tex (135,000 denier) formed of 45,000 filaments of 3.4 d. tex (3 denier) is obtained by wetspinning a copolymer containing 94% of acrylonitrile and 6% of methyl methacrylate, using dimethylformamide as solvent, and a mixture of dimethylformamide and water as coagulating bath. After washing with water and stretching, the filaments obtained are in the form of an aqueous gel containing 180 parts of water to 100 parts of polymer (reckoned as dry) and 1.2 parts of dimethylformamide.

The tow thus obtained is opened by the action of a turbulent gas and then introduced into a ventilated chamber on a perforated travelling belt. The temperatures in this chamber are 100 C. (dry bulb) and 6570 C. (wet bulb). The average speed of the air circulating through the chamber and through the perforated belt is 1.20 m. per second, which enables the wet filaments to have a temperature at least equal to that indicated by the Wet bulb thermometer.

The treatment in the chamber lasts 40 minutes. During 7,

its last stages the temperature of the filaments rises to 100 C., before they leave the treatment chamber,

The resulting tow may be stretched laterally to a width of 4 to metres, and forms a very fine network similar to a spiders web. Its strength is sufficient to support considerable loads without tearing, even in the wet state. It may be used to cover crops such as vines, in which its resistance to weathering is very valuable.

Its effectiveness may be further improved by passing it through a crimping device of the stuffing box type.

Example 2 A tow of 15,000 tex (135,000 denier) comprising 30,- 000 filaments of 5.6 d. tex (5 denier) is obtained in the same way as in Example 1. The filaments are obtained in the form of an aqueous gel containing 200 parts of water to 100 parts of dry polymer and 3 parts of dimethylformamide.

The tow is passed into a ventilated chamber as in Example 1, in which the temperatures are 110 C. (dry bulb) and 78 C. (wet bulb).

There is obtained a tow 'whOse filaments are sufliciently stuck together to enable it to be opened out to a width of 4 metres into a very fine network.

Example 3 A tow of 90,000 filaments in the form of an aqueous gel containing 220 parts of water to 100 parts of the same polymer as in Example 1 and 0.8 part of dimethylformamide is passed into a ventilated chamber, in which the temperatures are 120 C. (dry bulb) and 70 C. (wet bulb). The tow obtained is thereafter crimped in a compression chamber. A tow of 30,000 tex (270,000 denier) is obtained, which is formed of 90,000 filaments of 3.4 d. tex (3 denier), which are sufiiciently stuck together at intervals to enable it to be opened out into a very fine and very wide network.

Example 4 A tow identical to that employed in Example 2 is passed into a ventilated chamber, in which the temperatures are 80 C. (dry bulb) and 68 C. (wet bulb). The tow thereafter enters a relaxation zone at 130 C. and a crimping device of the stuffing box type.

The tow obtained can readily be spread out int-o a very fine continuous network.

Example 5 A tow of 135,000 filaments is obtained by wet-spinning a copolymer containing 97% of acrylonitrile and 3% of methyl acrylate into a bath consisting of water and dimethylformamid using dimethylformam'ide as solvent.

After washing and stretching, the tow, in the form of a gel containing 250 parts of water and 2.5 parts of dimethylformamide to 100 parts of dry polymer, is passed through a ventilated chamber at a temperature of 95 C. (dry bulb) and C. (wet bulb). A tow of 45,000 tex (405,000 denier) is obtained which can be opened out into an extremely wide network.

Example 6 A tow of 60,000 filaments in the form of an aqueous gel containing 180 parts of water and 3 parts of dimethylformamide to 100 parts of a copolymer consisting of 72% of acrylonitrile and 28% of vinylidene chloride is passed into a ventilated chamber, of which the first zone is moisture-saturated at a temperature of C. The tow circulates slowly through this zone, in which it stays for 30 minutes, whereafter it enters a second zone in which the temperatures are C. (dry bulb) and 40 C. (wet bulb). The total duration of the treatment is 45 minutes.

The tow is then steamed in the relaxed state at 130 C., and crimped in a stufiing box.

There is obtained a tow of 30,000 tex (270,000 denier) formed of 60,000 filaments of 5.6 d. tex (5 denier) stuck together at intervals and highly interwoven, which can be opened out into a very fine and very wide network.

Example 7 A tow of 45,000 filaments is obtained by wet-spinning a 20% solution of an acrylonitrile homopolymer in dim-ethylformamide into a coagulating bath consisting of a mixture of 40% of dimethylformamide and 60% of water. After counter-current washing with water and stretching by a total of 6.25 the filaments obtained are in the form of an aqueous gel containing parts of water to 100 parts of polymer (reckoned as dry) and 0.56 part of dimethylformarnide.

The tow thus obtained is opened by the action of turbulent gas jet and then introduced into a ventilated chamber on a perforated travelling belt. The dry and Wet bulb temperatures are both 75 C. at the inlet to the said chamber, whereafter the dry bulb temperature is raised to 100 C. and the wet bulb temperature lowered to 40 C. After treatment for about 45 minutes in this chamber, the tow is stabilised by an oven treatment at C. and then oiled and crimped in a cripming device of the compression chamber type.

There is obtained a tow whose filaments are welded together at intervals and which can be opened out to a width of 4 to 5 metres to give a very fine network of a spiders web type. Its strength is sufiicient to withstand considerable loads without tearing, even in the wet state. It may be used to cover crops such as vines, in which its resistance to weather influences is very valuable.

We claim:

1. Process for the production of a filamentary structure capable of being laterally extended to form a network, which comprises opening by means of an air jet a tow of stretched acrylonitrile polymer filaments, in which the acrylonitrile content of the polymer is at least 70%, and which is in the form of an aqueous gel containing, for each 100 parts by weight of polymer, 100-300 parts by weight of water and at least 0.5 part by weight of an organic solvent for the polymer, and subjecting the opened tow to heat treatment in a moist atmosphere wherein the wet bulb temperature of the atmosphere is 65-120 C. for a period of time sufficient to bring the temperature of the filaments to at least 65 C.

2. Process according to claim 1, in which the filaments have been formed by wet spinning using an aqueous coagulating bath.

3. Process according to claim 1, in which the filaments 5 have been stretched to at least 1.5 times their initial length.

4. Process according to claim 1 in which the filaments contain 1-5% (on the weight of the polymer reckoned as dry) of the organic solvent.

5. Process according to claim 1, in which the two is subjected to the temperature 65120 C. in a ventilated chamber.

6. Process according to claim 1, in which the dry bulb temperature in the chamber is 80-100 C.

7. Process according to claim 1, in which the tow contains 30,000 to 150,000 filaments.

6 References Cited UNITED STATES PATENTS 2,886,877 5/1959 Frickert et a1 156-467 3,101,245 8/1963 Fujita et al 264-346 3,151,011 9/1964 Troeleman et al 156-180 JULI'US FROME, Primary Examiner.

HERBERT MINTZ, Assistant Examiner.

US. Cl. X.R. 

